FIELD OF THE INVENTION
The present invention relates to a surge arrester with an elongated outer housing which consists of an insulator of polymeric material comprising at least one stack of a plurality of cylindrical arrestor elements, preferably made of zinc oxide varistor material, which are arranged one after the other in the axial direction of the arrestor elements between two metal electrodes which are each arranged at a respective end of the polymer insulator.
In connection with pollution, surge arresters are subjected to heavy radial electrical stresses. This is due to the differences between the internal voltage distribution which is controlled by the ZnO blocks and the external voltage distribution which is caused by the pollution. In arresters with polymer insulators, the high electrical stress is applied to the polymer material, with an ensuing risk of degradation of the polymer material. The stress in connection with pollution increases, in principle, with the length of the arrester. One way of reducing the risk of degradation of the polymer is to limit the electrical stress to a certain level, independently of the length of the arrester. This can be done, as is common in arresters with porcelain housings, by constructing the arrester in several mechanically separated parts (multi-part arrester), in which each arrester part comprises an insulating housing provided with metal flanges and comprising a stack of series-connected ZnO blocks. The metal flanges at the joint between adjacent arrester parts thereby form a galvanic connection between the stacks of blocks and the outer surface of the housing. This is, however, a uneconomical solution and, in addition, it makes the arrester unnecessarily long.